Genetic and structural studies revealed that the group d allotypic markers (d11 and d12) are associated with the hinge region of IgG heavy chains; the group e allotypes (e14 and e15) are IgG Fc markers. Our immediate objectives are, 1.) to determine the distribution and genetic association of the groups d and e specificities in the wild Australian rabbit population, 2.) to determine the distribution of genetic variants associated with the groups d and e allotypes among the North American cottontail rabbit and hare, and 3.) to assess the chemical basis of genetic variation for the domestic rabbit, cottontail and hare IgG allotypes where these exist.